This invention relates to marine drives, that by design operate partially above the water surface. Surface drives exhibit far less drag than their fully submerged counter parts and often used for high speed, marine powerboat competition.
Generally, marine surface drives, or xe2x80x9csurface piercing propeller drivesxe2x80x9d, can be divided into two categories; fixed and articulated. Fixed surface drives are stationary elements extending aft of the stern and require a separate rudder mechanism to direct thrust horizontally for directional control as illustrated in U.S. Pat. Nos. 4,854,903 and 4,689,026. The articulated versions as illustrated in U.S. Pat. Nos. 6,431,927, 4,790,782, and 4,544,362, has means that allow a drive assembly to move horizontally and/or vertically directing the angle of thrust as needed and generally do not require a separate rudder mechanism.
Disadvantages intrinsic to the xe2x80x9csurface piercing propeller drivexe2x80x9d are listed below:
(a) Poor reverse or backing performance, attributable to a xe2x80x9ccleaverxe2x80x9d style propeller design (optimized for surface running).
(b) Propeller-induced side forces, occurring when the top half of the propeller is exposed and a rotational drag of the submerged portion exerts a thrust perpendicular to the direction of forward travel. Large skegs (submerged, stationary fins) as illustrated in U.S. Pat. No. 5,667,415 and counter rotating propellers as illustrated in U.S. Pat. Nos. 4,790,782, and 4,544,362, can compensate for these side forces; however, both remedies result in a net increase of drag.
(c) Difficult optimization of engine performance and boat displacement to propeller size. For many this is trial and error. Most boat owners or operators do not have a broad selection of propellers on hand to evaluate. Nor would most have the equipment and time to evaluate many propellers.
(d) Axial instability occurs when a high speed planing boat equipped with a single, xe2x80x9csurface piercing propeller drivexe2x80x9d, is running at high speed in choppy conditions. The propeller induces an erratic thrust in both the forward direction and to a lesser degree, in the lateral direction as the drive encounters various peaks in the chop. The erratic thrust produced in the lateral direction induces a yaw or pitch to the boat. This affects performance and safety.
Various paddlewheel configurations may also be defined as surface drives, however, due to the invention of the xe2x80x9cscrew typexe2x80x9d propeller, few continue to have commercial application. A major disadvantage of the paddlewheel is the necessity to support the drive and most the paddlewheel above the surface. Efficiency is reduced dramatically when the paddlewheel operates with more than 20% of its diameter submerged. This occurs because a fixed paddle or blade produces thrust continuously as it rotates through the water, however, only thrust produced during the deepest part of the rotation efficiently moves the boat forward. A significant portion of available power is consumed accelerating water down ahead of the paddle wheel and lifting water up aft of the paddle wheel.
Attempts to produce more efficient and consistent thrust with a paddlewheel through the use of articulated blades have been tried as illustrated in U.S. Pat. Nos. 5,297,933, and 2,258,699. These patents and others like them, solve part of the problem by optimizing the contact angle of each paddle or blade relative to a desired direction of force, however the blade or paddle velocity parallel to this line of force is non-linear. Blade velocity (in the direction of the desired line of force) at a point where the blade crosses the horizontal centerline of the paddlewheel rotation is zero. In contrast, the blade velocity (in the direction of the desired line of force) at a point where the blade crosses the vertical centerline (at the bottom of the rotation) is at maximum and equals the rotating velocity of the paddlewheel. As a result the blades seem work against themselves. This problem becomes more pronounced when the paddlewheel is deeply submerged. For purposes of calculating available thrust of a given paddlewheel, an engineer must average the blade velocity as a function of its operating depths and the rotating velocity.
Many of the articulated designs of the prior art achieved the articulation through the use of complex planetary gear arrangements. These would be costly to build relative to a screw type propeller of similar thrust and would be difficult to maintain in a marine environment. In addition, it could be speculated that the friction loss through complex gear arrangements would offset any gains the inventor may have claimed. The large rotating masses associated with the planetary gear arrangements would prevent these designs from being used in a modern competitive powerboat environment.
Other commercial disadvantages of the paddlewheel include; large drive systems relative to screw type propellers, poor handling due to a flat blade design, and an obsolete stigma. The disadvantages of the paddlewheel have limited it to resort-style pedal boats and historic vessels, operating in relatively calm inland waters.
The obsolete paddlewheel, however, has inherent advantages over the xe2x80x9csurface piercing propeller drivexe2x80x9d such as the absence of propeller-induced side force and low relative drag possibilities.
The marine radial surface drive of the present invention exploits the advantages inherent in the paddle wheel and has several objects and advantages which are:
(a) to provide a radial surface drive that is simple to manufacture and operate and has wide commercial utility;
(b) to provide a radial surface drive with controlled and consistent thrust from a xe2x80x9cpaddle wheelxe2x80x9d configuration;
(c) to provide a radial surface drive of a xe2x80x9cpaddle wheelxe2x80x9d configuration which is relatively small compared with traditional paddlewheels and can be transom mounted in a conventional manner;
(d) to provide a radial surface drive with good reverse capabilities;
(e) to provide a radial surface drive which does not have a lateral or side force like a xe2x80x9csurface piercing propeller drivexe2x80x9d;
(f) to provide a radial surface drive without appendage drag;
(g) to provide a radial surface drive with the ability to trim the boat (alter the vertical angle of delivered thrust) while underway;
(h) to provide a radial surface drive with the ability to limit the magnitude of delivered thrust while underway;
(i) to provide a radial surface drive that by design is open, and easy to inspect and service;
(j) to provide a radial surface drive that is stable under extreme acceleration because the rotation of the drive is radial and not axial;
The marine radial surface drive of the present invention combines known paddlewheel and surface drive concepts with several unique features. The result is a design that is versatile and easy to manufactured with current knowledge and machinery.
As will be seen in the drawings, one example of this, is the unique blade shape and profile which is a major contributor to the overall performance of the surface drive of the present invention. The curved shape of the blades cause them to function under load like turbine vanes, delivering thrust throughout the submerged portion of a rotation much more efficiently than flat blade designs. Two discrete curves are visible in each blade""s profile, these allow for efficient operation at multiple depths and provide stability in choppy waters. A slight concave curve is featured along each blade""s axial plane, which provides lateral stability under acceleration.
Another unique feature is the placement of an eccentric cam within the blade support cylinder. This xe2x80x9cload camxe2x80x9d allows the tip velocity of the blades to be controlled and regulated during the submerged portion of the rotation. The shape of the cam allows the thrust delivered by the drive to be tailored to suite boat displacement and engine efficiency. By changing the position of the cam, the blade""s tip velocity and angle can be changed while the boat is underway. Cams with different profiles can be exchanged to suite specific applications or power improvements of a given boat.
Further objects and advantages will become apparent from a consideration of the ensuing description and drawings such as the articulated drive support and shroud. These features are essential to the preferred embodiment, which is a design optimized to replace stern drives within existing boat designs and configurations.
The versatility of the present invention allows for a variety of configurations including; twin drives with a single inboard engine, and twin drives with two inboard engines. As will be seen in the ensuing drawings, boat designs can be engineered around the radial surface drive in a highly stylized manner.
It is the purpose of this invention to provide a surface drive, which affords the competitive and commercial advantages of the xe2x80x9csurface piercing propeller drivexe2x80x9d, while eliminating the inefficiencies and instabilities associated with propeller induced side forces. Furthermore, it is the purpose of this invention to provide a radial surface drive that by design, allows an operator of a boat so equipped with said drive, to actively control and adjust the relative magnitude, angle and elevation of the thrust delivered by said drive.
The radial surface drive of the present invention is lightweight, easy to fabricate, and requires low maintenance. The present invention may be made from corrosion-resistant materials such as brass, stainless steel, aluminum, and composites to extend the useful life of the apparatus.
The radial surface drive of the present invention has useful application within marine powerboat competition, as well as many useful leisure and/or commercial applications.
A marine radial surface drive of the present invention does not use a screw type propeller operating upon an axial rotation. Instead, such apparatus comprises a plurality of articulated blades of unique shape, affixed to a central hub operating upon a radial rotation. In the present invention, the radial surface drive is affixed to a drive axle that is perpendicular to the centerline or keel of the boat and is secured within an adjustable support member extending aft of a transom and above the surface. A cam within the drive""s hub manipulates the angle of the blades during a selectable portion of a rotation and is controlled by the operator. In the preferred embodiment, the aft support member pivots vertically at the transom; hydraulic actuators affixed to the transom and the support member allow operator control of the vertical elevation of drive. In the preferred embodiment, a rudder assembly is attached to the trailing end of the support member. A shroud encloses the forward portion of the drive for safety as well as decreasing blade cavitation at high speeds through aeration. These features are not combined in any known prior art.